It is conventional to calibrate a clinical analyzer for a given assay and a given lot of test elements using several known calibration liquids with known analyte concentration (or activity). These liquids are dispensed on test elements from that lot, and responses are determined. The determined responses and the known concentrations are then used to compute calibration coefficients, using a known equation, so that such coefficients and equation can be used to calculate unknown concentrations using the responses generated from patient samples, using the same lot of test elements. For example, in a glucose test, it is conventional to use the equation EQU Concentration=A0+A1.multidot.g1(Response)+A2.multidot.g2(Response).sup.K( 1)
where g1 and g2 are cubic splines, K is an integer, usually=2, and A0, A1 and A2 are specific calibration coefficients. (See the "Principles of Calibration" section from the E700 Operators Manual.) Equation (1) has been published in connection with the analyzers available from Eastman Kodak Company under the registered trademark of "Ektachem". For simplicity, g(R) is hereinafter referred to simply as "response", so that "R" is either the raw response or a cubic spline function of the raw response.
It is also known that such calibration coefficients could be predetermined at the factory in some instances, and passed on to the purchaser of a given lot of test elements for that assay, to avoid making the user recalibrate each time a new lot is shipped. Such information is passed on in a variety of ways.
The methods of passing on calibration information to the user include printed information and magnetic discs. Analyzers available from Eastman Kodak Company use a calibration diskette to transfer calibration information to users but the calibration coefficients are not included on this diskette. It is not economically feasible to send a calibration diskette with each lot of slides for each assay, so calibration coefficients are not sent to the customer via a diskette. Lot specific calibration coefficients can be transferred to the customer if the information is incorporated on the actual test element or its container. Two possible ways of transferring this information are by bar code or magnetic strip, as described in "Boehringer Mannheim detects high cholesterol with the Reflotron diagnostics system", Directions, Vol. 6, No. 4, fourth quarter, 1989, or in Japanese Kokai 60/93351. With single bar code strips and magnetic strips there is a limited number of digits, e.g., six, available to pass the calibration coefficients, yet the purchaser requires accurate values for the calibration coefficients A0, A1 and A2. If one is using a six decimal digit bar code, then A0, A1 and A2 must be passed to the purchaser using only six decimal digits. The obvious solution is to specify A0, A1 and A2 using two digits each. This means that each of these must be accurately specified by using the digits 0 to 99, the maximum possible in a 2-digit decimal finite number. Unfortunately, the specific solutions of A0, A1 and A2 can vary much more than this in a given assay, say glucose, because these coefficients are a function of the cubic splines that are used to best-fit the particular chemistry of a particular lot of test elements, to the data. Yet, bar coding is by far the preferred method of conveying the information of these coefficients, since that can be easily printed on each set of test elements or the package therefor. Nevertheless, it is well-recognized that a single strip of bar-coding is insufficient to portray the parameters of the calibration coefficients, as explained in Japanese Kokai 60/93351.
Of interest is the fact that the aforesaid '351 application attempts to solve the problem by providing, not a single strip of bar-coding, but rather, a triple strip of bar-coding, so as to allegedly increase the number of digits available to 1728 (12 cubed). However, this approach is unsatisfactory since it requires both a much larger label for triple the amount of codes, as well as a much more sophisticated bar code reader.